Leakage of fluid from a rod or a plunger pump to the environment is highly undesirable, particularly in the case of oil wells when the leaked fluids will contaminate the vicinity of the well, and possibly even run into streams in the area. In addition to contamination, the leakage of the oil results in loss of valuable natural resources. This problem is particularly acute where the well is on a pumping system where a polish rod reciprocates through a packing gland at the top of the production tubing in order to operate a downhole pump. Most all of such pumping systems are examined and serviced only occasionally, so that leakage can go undetected for a considerable length of time before it is discovered.
Another common source of leakage is past the packing gland of a multiplex plunger pump that is used in various hydraulic pumping systems, for example a system that is used to circulate power oil under high pressure to a hydraulically operated downhole pump, and systems such as transfer and pipeline pumps that operate on a substantially continuous basis. Hereagain, such pumps usually include a reciprocating plunger that extends into a pump chamber through a stuffing box, and operates in a manner such that the fluid being pumped is drawn in through the inlet to the chamber during reciprocation of the plunger in one direction, and is forced out through an outlet from the chamber under high pressure during reciprocation of the plunger in the opposite direction. The high pressures involved, and the occasional abrasive nature of the fluids being pumped, have made it extremely difficult to provide a leak-proof packing gland or stuffing box apparatus that will contain the pumped fluid during operation over an extended length of time.
Although not directed to the concepts of the present invention, attempts to improve the seal between a gland and a rod are shown in U.S. Pat. Nos. 2,155,628 and 3,602,613. The '628 patent illustrates a spring-loaded piston which transmits submergence pressure to an annular cavity outside a number of packing rings that are axially compressed between thrust faces and biased inward by garter springs. The cavity pressure is maintained by the action of the piston spring at a level which exceeds submergence pressure by a selected amount, so that all peripheral edges of each packing ring are extruded outward by the garter spring. In another embodiment which is disclosed in this patent as being applicable primarily to high rotary speed applications, the spring and piston cause radial inward pressure on the packing rings to exceed chamber pressure by some selected amount, so that in addition to such extrusion the rings always "hug" the rod tightly. However, this '628 patent is not pertinent to the concept of balancing fluid pressures across a secondary in a stuffing box, and employs a packing ring construction that does not lend itself to such concepts. The '613 patent discloses a seal assembly where a pair of metal seal bushings are used, and an auxiliary pump is employed to apply pressure between them in a manner such that bushing-to-rod clearances are reduced. This patent also fails to teach or to suggest the balancing, or substantially, of fluid pressures in a manner such that an unknown fluid has practically no tendency to leak past a secondary seal while a primary seal is used to contain the pressure of a known fluid.
The general object of the present invention is to provide a new and improved stuffing box and pressure transmitter combination for preventing leakage of fluid past a plunger or rod that reciprocates under pressure with respect to the gland.
Another object of the present invention is to provide a new and improved seal assembly of the type described that includes primary and secondary seals for preventing fluid leakage along the rod, and where one of these seals is subjected to balanced pressures by a transmitter that transmits pump chamber pressure to the outer side of the secondary seal to prevent movement of pumped fluids under pressure therepast.
Still another object of the present invention is to provide a new and improved seal assembly of the type described where the seal assembly includes primary and secondary seals are separated by a chamber that contains a clean lubricating oil, and where the transmitter includes piston means which transmit the pressures of the pumped fluid to the lubricating oil in the chamber in order to balance fluid pressures across the secondary seal, thereby allowing the primary seal to prevent leakage of a known fluid, i.e. the lubricating oil.